The present invention relates to blow molding apparatus and more particularly to a reheat blow molding machine including an improved preform loader, oven transport assembly, preform transfer assembly and mold substation.
A wide variety of containers including those for carbonated beverages and food products, are manufactured using blow molding processes. Various plastics may be used including resins which are biaxially orientable. Such resins include polyethylene terephthalate (PET) and polypropylene (PP). In reheat blow molding processes, the plastic is first injection molded to form a preform or parison. The preforms have a test tube configuration, an external cap thread at an upper open end thereof, sometimes a pilfer proof ring and/or a support ring. The premanufactured preforms are reheated in an oven prior to the blow molding operation. The oven receives the preforms and heats them to a desired temperature at which the plastic will biaxially orient and/or stretch in the blow molding operation.
In existing machines, the heated preforms are transferred from the oven to a blow molding station by a carriage or reach and take subassembly. The blow molding station includes a vertically split mold which may define a plurality of cavities The preforms are properly positioned and the mold is closed. A blow head delivers high pressure air to the preforms to form them into the container configuration. The blow head may incorporate center rods which stretch the preform during the blow molding step. After the molding is completed, the mold is opened and formed containers are ejected from the machine. U.S. Pat. No. 4,784,253 entitled BLOW MOLDING APPARATUS and issued on Nov. 15, 1988 to Gibbemeyer and U.S. Pat. No. 4,310,282 entitled DELAY STRETCH AND BLOW MACHINE SYSTEM and issued on Jan. 12, 1982 to Spurr et al disclose examples of prior machines.
Typically, the preforms are delivered to an oven by a descrambler and orientation apparatus. The preforms are usually handled by the threaded neck and the lower portion of the preform is reheated as it passes through an oven structure. Continuous or endless chains including a collet arrangement may be used to rotate the preforms as they pass through the oven. In other arrangements, individual pallets or shuttles are used. The pallets arranged in tandem, abutting relationship, are moved through the oven in a stepwise fashion.
A blow molding apparatus employing a continuous conveyor and a plurality of couplings for transporting preforms through an oven is disclosed in U.S. Pat. No. 3,958,685 entitled COUPLING FOR HANDLING WORK PIECE, CONVEYOR COMBINED THEREWITH, AND METHOD which issued on May 25, 1978 to McDonald et al. In such apparatus, a coupling or collet receives a preform. The coupling is mounted on a continuous chain conveyor. Provision is made for rotating the preform as the coupling passes through the oven in order to insure uniform heating prior to the blow molding step.
An example of a pallet or shuttle assembly for a blow molding machine may be found in U.S. Pat. No. 4,684,012 entitled BLOW MOLDING PALLET ASSEMBLY and issued on Aug. 4, 1987 to Feddersen. The pallet is used to transfer preheated preforms from an oven through a blow mold and then to a discharge location.
Many different types of preform transfer mechanisms have been developed One such mechanism is disclosed in commonly owned U.S. Pat. No. 4,709,803 entitled PREFORM TRANSFER MECHANISM and issued on Dec. 1, 1987 to Swiderski. The preform transfer mechanism disclosed therein includes a slide block or carriage which is reciprocated towards and away from a blow mold station. The carriage supports a plurality of jaw assemblies. Preform receiving and locating means are provided to receive the preforms from an oven and position them properly for engagement by jaws of the transfer mechanism. Provision is made for compensating for differences in preform size, within limited tolerances.
Problems heretofore experienced with existing machines include mechanical complexity, inherent limitations on production rates and limited versatility as to the size of the product produced. Available machines set up to make beverage bottles are not readily converted to manufacture containers having wide mouths. Typical beverage containers have a mouth with a diameter of 28 millimeters. Wide mouth containers usable for many food products have diameters up to 89 millimeters. Larger containers may also have a capacity of up to 1 gallon or 4 liters. A need exists for a machine of reduced complexity which will have increased or improved production capabilities and which is readily changeable to different size containers.